Crustal deformation across and beyond the Los Angeles basin from geodetic measurements

We combine 6 years of Global Positioning System (GPS) data with 20 years of trilateration data and a century of triangulation, taped distance, and astronomic azimuth measurements to derive 66 interseismic station velocities in the greater Los Angeles region. We interpolate the velocities to construct a regional strain rate map beyond the Los Angeles basin. Our results generally agree with the model proposed by the Working Group on California Earthquake Probabilities in 1995. Important regional findings of this study are as follows: (1) There is a significant N-S convergence and EW extension, about 0.22 and 0.17 +/- 0.05 mu strain/yr, respectively, for the two components, along the southern frontal fault system of the San Gabriel Mountains. (2) The crustal deformation around the Big Bend of the San Andreas fault (SAF) cannot be explained solely by wrench-style motion across the SAF. Remaining motion could be part of a NW-SE extension which is the response to NE-SW compression in the central Transverse Ranges region. Alternatively, it could be caused by left-lateral faulting on an oblique blind thrust beneath the San Gabriel Mountains. (3) Low strain rates are found along the Elsinore fault and Newport-Inglewood fault. (4) North-south compression decreases from the Raymond Pill fault westward to the Santa Monica fault. There is little east-west extension along this fault system.